This invention relates to the packaging of products containing oils in packages using flexible sheet materials. This invention is particularly applicable to such products which are sensitive to moisture, and which require that the package material serve to protect them from infusion of moisture from the outside environment. Such products have conventionally been packaged in glassine-based sheet structures. More recently, all-plastic structures have been used to advantage to improve product quality through increased protection from infusions from the outside environment. The industry has been struggling with the problem that certain ones of the plastic packaging structures, while providing excellent protection to the product, are cockling at some point during the normal shelf life of the product. The term cockling as used herein means to have ripples or puckers, usually due to some uneven tension, and the uneven tension yielding a surface that is not smooth, but, rather, is uneven and wavy.
Thus it is an object of this invention to provide a package having a plastic sheet structure which does not cockle upon contact with oil.
It is another object to provide, in such a package, good protection from gaseous infusions from the outside environment; especially infusions of oxygen and moisture vapor.